My PC is a 2.4G Celeron, 512M Ram with Win XP Pro sp1.

I was very happy with its throughput. So I bought the same model again. There is a slight difference between the two modems, the old modem used Agere 1048C-TV5 and CSP1034C (44pin quad sided surface mount) chips, the new model uses Agere 1048C-TV5 and CSP1034S (38pin Dual In Line surface mount) chips.
To install the new modem I just shut off the PC, unplugged the old modem, plugged in the new modem in the same PCI slot, and powered up the PC. Win XP Pro did not recognise any change in the hardware. Which is what I expected, given that the two Agere chips on the old and new modem, have almost the same part numbers.

The new modem would only connect at 31.2kbps.

I was very annoyed, I tried updating the drivers from 8.18 to 8.30, even though I found that the old modem always worked better with the 8.18 drivers.

The new modem still won't connect at as high a speed and doesn't give as high a receive throughput.

When I do an ATI11 after the modem has disconnected, I notice that the new modems Receive Frame Error rate is always 3 or 4 times higher than the old modem ever got.

Here's a log from the new modem

ati3
Agere V.92 Data+Fax Modem Version 8.30

OK
ati5
8.30,0,01,11C1,044C,11C1,044C

OK
ati11

Description Status
--------------- ------------
Last Connection V.90
Initial Transmit Carrier Rate 28800
Initial Receive Carrier Rate 45333
Final Transmit Carrier Rate 28800
Final Receive Carrier Rate 45333
Protocol Negotiation Result LAPM
Data Compression Result V42bis
Estimated Noise Level 1566
Receive Signal Power Level (-dBm) 4
Transmit Signal Power Level (-dBm) 14
Round Trip Delay (msec) 5
Press any key to continue; ESC to quit.

Description Status
--------------- ------------
Near Echo Level (-dBm) NA
Far Echo Level (-dBm) NA
Transmit Frame Count 41905
Transmit Frame Error Count 0
Receive Frame Count 61840
Receive Frame Error Count 18050
Retrain by Local Modem 2
Retrain by Remote Modem 0
Call Termination Cause 0
Robbed-Bit Signaling 00
Digital Loss (dB) 0
Remote Server ID NA
Connection Time (sec) 19.500

OK

Here's a typical log from the old modem

ati3
LT V.92 Data+Fax Modem Version 8.18

OK
ati4
71

OK
ati5
8.18,0,01,11C1,044C,11C1,044C

OK
ati11

Description Status
--------------- ------------
Last Connection V.90
Initial Transmit Carrier Rate 28800
Initial Receive Carrier Rate 48000
Final Transmit Carrier Rate 28800
Final Receive Carrier Rate 45333
Protocol Negotiation Result LAPM
Data Compression Result V42bis
Estimated Noise Level 311
Receive Signal Power Level (-dBm) 7
Transmit Signal Power Level (-dBm) 14
Round Trip Delay (msec) 5
Press any key to continue; ESC to quit.

Description Status
--------------- ------------
Near Echo Level (-dBm) NA
Far Echo Level (-dBm) NA
Transmit Frame Count 53515
Transmit Frame Error Count 2
Receive Frame Count 29270
Receive Frame Error Count 6909
Retrain by Local Modem 1
Retrain by Remote Modem 0
Call Termination Cause 0
Robbed-Bit Signaling 00
Digital Loss (dB) 0
Remote Server ID NA

OK

What's the normal good RX Frame Error count supposed to be.
Could this increased Receive Frame Error count be causing the reduction in my receive throughput ?

Do you think the new modem might have some kind of probelm that is causing this high Rx Frame Error count ?

Frame, and frame error - these counters have maximum value of 65535, which, if reached, will return to zero and start counting over - which makes use of these diagnostics tricky.
What I like to do is check the diagnostics after a relatively short connection (of only a few minutes) so that there's reasonable certainty that the values are valid.

Frame errors - these #s should be as low as possible; frame errors require retransmission of data which can result in reduced throughput. Generally, frame errors can be reduced by reducing/limiting the maximum connect speed.
It's possible that the new modem is 'slightly defective'; or, more susceptible to interference from other components of your PC - you might want to try it in another PCI slot; it's also possible that the line cord from the modem to line is a factor (routing of it; make sure it has only 2 wires connected to the plugs).

Using Hyperterminal w/ new modem - issue command
AT+GCI?
what response do you get?

The reason I only do the ATI11 commands after the call is finished is because I don't know how to send commands to the modem when it's still connected, can you tell me how to do this ? I have vague recollections that you can use Hyperterm with some kind of AT command to interrupt the modem from data transfer mode, was it +++ ?, but can't remember command to resume data transfer ?

The line cord was not changed, I just unplugged it from the old modem and rested it on the desk about 10cm from the back of the PC, installed new modem in the same slot and plugged the cord into the new modem. The cords routing is unchanged, it's unlikely that the amount of noise being induced into the cord would have changed, unless it was coming from the new modem but I don't think that's likely.

Here's the new modem log of a Win XP modem properties query, which was taken after the modem session had ended.

ATQ0V1E0 - OK
AT+GMM - H.324 video-ready rev. 1.0
AT+FCLASS=? - 0,1,8
AT#CLS=? - COMMAND NOT SUPPORTED
AT+GCI? - +GCI:09
AT+GCI=? - +GCI:(09,0F,31,3C,3D,42,7B,59,7E,82,
A0,A5,A6,B4,0A,00,26,61,6C,9C,
A9,54,8B,B5,57,50,20,73,53,BC,
89,46,51,AE,9F,8A,2E,69,16,1B,
2D,52,B8,58,98,84,07,14,25,27,
35,85,88,BB,87,B7,8C,49,2B,7F,
68,B3,B2,36,0E,48,62,8E,A1,83,
0D,64,70,77,AD)
ATI1 - B3E5
ATI2 - OK
ATI3 - Agere V.92 Data+Fax Modem Version 8.30
ATI4 - 71
ATI5 - 8.30,0,01,11C1,044C,11C1,044C
ATI6 - OK
ATI7 - OK

Here's the same thing from the old modem for comparison

ATQ0V1E0 - OK
AT+GMM - H.324 video-ready rev. 1.0
AT+FCLASS=? - 0,1,8
AT#CLS=? - COMMAND NOT SUPPORTED
AT+GCI? - +GCI:09
AT+GCI=? - +GCI:(09,0F,31,3C,3D,42,7B,59,7E,82,
A0,A5,A6,B4,0A,00,26,61,6C,9C,
A9,54,8B,B5,57,50,20,73,53,BC,
89,46,51,AE,9F,8A,2E,69,16,1B,
2D,52,B8,58,98,84,07,14,25,27,
35,85,88,BB,87,B7,8C,49,2B,7F,
68,B3,B2,36,0E,48,62,8E,A1,83,
0D,64,70,77,AD)
ATI1 - B3E5
ATI2 - OK
ATI3 - LT V.92 Data+Fax Modem Version 8.23
ATI4 - 71
ATI5 - 8.23,0,01,11C1,044C,11C1,044C
ATI6 - OK
ATI7 - OK

I've been unsuccessful trying to find any info about the CSP1034S and CSP1034C-J, other than some mention on the Agere site that says the CSP1034C has a controlable amplifier. I wonder if the 8.30 drivers are mis-controlling
this amplifier ?

As for getting diagnostics mid-call, you can't do this on a regular PPP/Internet session, but you could if your session were Hyperterminal in which case the
+++
sequence would drop you to command mode without disconnecting.

I am in Australia.

Not sure why it chose New Zealand, I'm sure I never specified my location as NZ anywhere on my PC, nor on the Netcomm web site where I downloaded the drivers from ?
NZ is probably just a PABX off Australia anyway :-)

I just checked the DUN properties while connected and it has the country field greyed out, I'll input Australia before my next connection.